I have to develop a project that basically receives and sends data on a Bluetooth LE module, and then changes the stream a bit and re-sends or receives that information on another radio module in the same case. The frequencies will be different. The Bluetooth needs to only transcieve a few feet, but the other frequency will have a somewhat longer range, probably 2 to 4 miles. I plan to have the modules physically on the same PC board, but on opposite ends. This will be in the US and possibly Canadian and EU / UK markets later.

I plan to use a 4 layer PC board of about 4 x 3 inches. It will be powered by rechargeable Lithium battery so I need to to run it on about 3.5 to 4 volts.

I had planned to use a PCB antenna for the BTLE but maybe an attachable antenna to the module for the other radio.

Are there many special issues I'll need to look out for when using two radios at once?

What other gotchas will I have to look out for? If I use modules that are both already certified with the FCC will I still need to receive intentional radiator certification? or just passive radiator?

I don't believe this is the same as this question this question because I'm going to use a lower frequency for the other radio, possibly the ISM bands.

There will not be two Bluetooth modules on the same board.

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    \$\begingroup\$ It is impossible to predict issues you might have. It also depends on what the other radio (for the 2 to 4 miles range) will be. possibly the ISM bands Uhm since these are the only ones that are license free I don't think you have much choice. You're not allowed to use other bands. I have yet to see a solution for that 2 to 4 miles range suitable for consumer equipment (i.e. license free). But please prove me wrong. \$\endgroup\$ – Bimpelrekkie Mar 13 '17 at 20:54
  • \$\begingroup\$ @FakeMoustache there's WAN devices; LoRa and competitors spring to mind. They, of course, all work in ISM bands, but unlike OP thinks, there's not only one ISM band (at 2.4 GHz) but a lot – and some of them are at lower frequencies. \$\endgroup\$ – Marcus Müller Mar 13 '17 at 20:59
  • \$\begingroup\$ Indeed there are cellular based solutions to get the 2-4 mi. range. However I was assuming OP was not considering cellular solutions since there the range is basically worldwide as long as you're in range. And zero when you're not. They depend on a base station being present in range. \$\endgroup\$ – Bimpelrekkie Mar 13 '17 at 21:46
  • \$\begingroup\$ Yes, exactly - I want to use LoRa on the ISM bands. I want to use the lower frequencies than the 2.4 ghz. \$\endgroup\$ – mark b Mar 13 '17 at 21:47
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    \$\begingroup\$ You will definitely have to get the board re-certified by a testing lab with multiple radios in one case. I once did a project with GSM, Bluetooth, and ISM all on one board. Took a couple of tries to get it to pass. I had the modules as far apart from each other as I could. \$\endgroup\$ – tcrosley Mar 14 '17 at 0:28

If you require concurrent transmission by one radio, with reception by the other radio, you'll need to evaluate how the Transmitter phasenoise or spurious will de-sense the receiver. Sharp transmitter filters (cell towers use these) and sharp receiver filter (ditto) permit lots of friendly concurrent activity. The Transmitter phasenoise, however, should it overlap the receiver frequency, will de-sense.

  • \$\begingroup\$ Not sure how this system-level type answer helps here. What you write is true but I doubt if OP has even the slightest idea what you're talking about. I doubt he understands phasenoise. And there's little need if you're not building the transceivers yourself (which OP is not). \$\endgroup\$ – Bimpelrekkie Mar 14 '17 at 6:50
  • \$\begingroup\$ I used to do this back in the late 70s and 80s. I used to burn my own PC boards back then using sunlamps and photoresist and most things I did were analog. But back then, HF stuff was not done on PC boards much. I understand it. Then I left electronics in mid 80s to be a programmer only - and am now getting back into electronics. So I understand it. I used to write firmware for high speed digital filters. \$\endgroup\$ – mark b Mar 14 '17 at 15:47

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